The present invention relates nuclear magnetic resonance (NMR) imaging; and more particularly, to a novel two dimensional B1-gradient NMR imager and methods for non-invasive spectroscopic and imaging investigations of the internal distribution and speciation of materials of fluid, solid, and semisolid objects in two spatial dimensions.
Nuclear magnetic resonance (NMR) analysis is a powerful method by which to determine chemical structures and to examine reaction dynamics in a diversity of chemical and biochemically systems. Magnetic resonance imaging (MI) is also a well established medical tools for non-invasive diagnostics of internal organs in living systems.
For example, U.S. Pat. No. 5,574,370, issued Nov. 12, 1996 to Woelk et al. discloses a toroid cavity detection (TCD) system for determining the spectral properties and distance from a fixed point for a sample using Nuclear Magnetic Resonance. The detection system consists of a toroid with a central conductor oriented along the main axis of the toroidal cylinder and parallel to a static uniform magnetic field, B0. An RF signal is inputted to the central conductor to produce a magnetic field B1 perpendicular to the central axis of the toroid and whose field strength varies as the inverse of the radial position within the toroid. The toroid cavity detection system can be used to encapsulate a sample, or the detection system can be perforated to allow a sample to flow into the detection device or to place the samples in specified sample tubes. The central conductor can also be coated to determine the spectral property of the coating and the coating thickness. The sample is then subjected to the respective magnetic fields and the responses measured to determine the desired properties.
U.S. Pat. No. 6,046,592, issued Apr. 4, 2000 to Rathke et al., discloses a near-electrode imager for employing nuclear magnetic resonance imaging to provide in situ measurements of electrochemical properties of a sample as a function of distance from a working electrode. The near-electrode imager uses the radio frequency field gradient within a cylindrical toroid cavity resonator to provide high-resolution nuclear magnetic resonance spectral information on electrolyte materials.
U.S. Pat. No. 6,191,583, issued Feb. 20, 2001 to Gerald II, discloses a toroid cavity detector that includes an outer cylindrical housing through which extends a wire along the central axis of the cylindrical housing from a closed bottom portion to the closed top end of the cylindrical housing. In order to analyze a sample placed in the housing, the housing is placed in an externally applied static main homogeneous magnetic field (B0). An RF current pulse is supplied through the wire such that an alternately energized and de-energized magnetic field (B1) is produced in the toroid cavity. The B1 field is oriented perpendicular to the B0 field. Following the RF current pulse, the response of the sample to the applied B0 field is detected and analyzed. In order to minimize the detrimental effect of probe ringing, the cylindrically shaped housing is elongated sufficiently in length so that the top and bottom portions are located in weaker, fringe areas of the static main magnetic field B0. In addition, a material that tends to lessen the effect of probe ringing is positioned along the top and bottom ends of the toroid cavity. In another embodiment, a plug is positioned adjacent the inside of the top and bottom ends of the toroid cavity so that the sample contained in the toroid cavity is maintained in the strongest and most homogeneous region of the static magnetic field B0.
The subject matter of each of the U. S. Pat. Nos 5,574,370, 6,046,592, and 6,191,583 is incorporated herein by reference.
A special type of NMR detector, a Magic Angle Spinning NMR (MAS NMR) detector can be used to examine solids. Other researchers have used magic angle spinning NMR to study heterogeneous catalyzed reactions at elevated pressures. Several technical problems, however, limit the use of this technique. For flow-through reactions, which include most industrial processes, the need for rotating seals limits attainable pressures to xcx9c80 pounds per square inch (psi) (xcx9c5.5 kPa). Glass, plastic, or ceramic pressure vessels are brittle and further limit pressures to less than 100 psi (6.9 kPa). Metal containers are thus necessary for the high pressures used in industrial applications, but they require that a radio frequency (RF) detector coil be positioned inside the container. Enclosing the RF coil in a metal container complicates the apparatus significantly because the electromagnetic field generated by the RF coil strongly interacts with the electronically conductive surfaces. This electromagnetic interaction reduces the sensitivity and the overall performance of the detector.
U.S. Provisional application 60/308,412 filed Jul. 27, 2001 by Rex E. Gerald II, Robert J. Klingler, Jerome W. Rathke, entitled ROTATIONAL EXCHANGE GRADIENT IMAGER FOR IN SITU MAGNETIC RESONANCE ANALYSIS IN ULTRACENTRIFUGE SEDIMENTATION OF BIOLOGICAL MATERIALS AND RHEOLOGY INVESTIGATIONS discloses a detecting method and detector that expands the capabilities of Nuclear Magnetic Resonance (NMR) analysis, allowing non-conventional materials to be examined using NMR in real time. A Rotational Exchange Gradient Imager (REGI) allows for real-time, in situ investigation of materials subjected to the effects of centrifugal force by nuclear magnetic resonance (NMR) analysis. The REGI comprises a cylindrical stator formed of an electrically conductive, non-magnetic material, a rotor contained in the cylindrical stator formed of an electrically non-conductive, non-magnetic material, and a conductor located along a central axis of the cylindrical stator. A sample is contained within the rotor. The stator and central conductor serve to generate the RF magnetic field for NMR analysis. The rotor containing the sample is rotated within a stable air bearing formed between the cylindrical stator and rotor. In one embodiment, the rotor is driven by high-pressure carrier gas jet containing one or more reactants delivered to the inside of the stator via a closed loop. The central conductor and the stator and rotor are held at a predefined magic angle. In other embodiments, an air jet or a mechanical drive assembly drives the rotor. The mechanical drive assembly is coupled to the rotor and includes a drive motor and a drive gear. Throughout the analysis, the sample contained within the rotor is rotated, stopped, started, and rotation direction reversed with accurate and precise control of the rotation frequency and rotor position. The REGI allows in situ NMR analysis and imaging of processes not possible before; for example, sedimentation of proteins, deformations of soft materials, lubrication, and heterogeneous catalysis under high flow-through gas pressure. The REGI can provide highly detailed information, through NMR spectroscopy and imaging, in diverse fields of science including molecular biology, rheology, tribology, and heterogeneous catalysis.
A principal object of the present invention is to provide an improved nuclear magnetic resonance (NMR) imaging device and methods for non-invasive spectroscopic investigations and imaging of the internal distribution and speciation of materials of fluid, solid, and semisolid objects in two spatial dimensions.
Other important objects of the present invention are to provide such improved NMR imaging device and imaging methods substantially without negative effect; and that overcome some disadvantages of prior art arrangements.
In brief, a two dimensional B1-gradient NMR imager and methods for non-invasive spectroscopic investigations and imaging of the internal distribution and speciation of materials of fluid, solid, and semisolid objects in two spatial dimensions are provided. The two dimensional B1-gradient nuclear magnetic resonance (NMR).imager includes a hollow electrically conducting cylinder having opposite open cylinder ends. A first cap and a second cap are secured to the opposite open cylinder ends to define a toroid cavity and enclose a sample. An elongate central conductor extends along a central axis of the toroid cavity. A magnet generates an externally applied static main magnetic field B0 to the toroid cavity and the enclosed sample. An RF signal transmitter/receiver coupled to the conductor generates a magnetic field B1 within the toroid cavity and receives a sample response to the magnetic fields B0 and B1. A pivot angle position controller coupled to the cylinder adjusts a pivot angle position of the toroid cavity and enclosed sample to vary an angle xcex8 between the magnetic field B0 and the central axis of the toroid cavity. A positional rotation controller coupled to the cylinder positions the toroid cavity and enclosed sample at variable angular orientations xcex6 relative to an initial position and a plane formed by the externally applied static main magnetic field B0 and the central axis of the toroid cavity. A computer operatively controls the RF signal transmitter/receiver, the pivot angle position controller and the positional rotation controller, sequentially receiving sample responses. The sample response data is processed to produce a two-dimensional image.
In a first operational embodiment of the invention, sample responses are received at each of a plurality of different angles xcex8 between the magnetic field B0 and the central axis of the toroid cavity at a first angular orientation xcex6; and then sample responses are received at each of the plurality of different angles xcex8 at a second different angular orientation xcex6.
In a second operational embodiment of the invention, the angle xcex8 between the magnetic field B0 and the central axis of the toroid cavity is set to 90xc2x0 and sample responses are received at each of a plurality of different angular orientations xcex6.
In a third operational embodiment of the invention, the angle xcex8 between the magnetic field B0 and the central axis of the toroid cavity is set to 54.7xc2x0 and sample responses are received at each of a plurality of different angular orientations xcex6.